A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that instance, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g. comprising part of, one, or several dies) on a substrate (e.g. a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at one time, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.
In order to decrease the critical dimension of devices, a lithographic projection apparatus may be arranged with a radiation source for EUV radiation. The radiation source for EUV radiation may be a discharge plasma radiation source, in which a plasma is generated in a substance (for instance, a gas or vapor) between an anode and a cathode and in which a high temperature discharge plasma may be created by Ohmic heating by a (pulsed) current flowing through the plasma.
Existing discharge based EUV sources for EUV lithography are based on a plasma pinch effect. As an additional product of the plasma pinch, fast ions appear which may sputter optics in the lithography apparatus. The amount and distribution of energy of fast ions in an EUV radiation source depend on the amount of energy in one pulse. The larger the energy of one pulse, the larger the number of fast ions and their mean energy and thus the larger the sputtering rate of the optics.